Interlocking IM nails with outer screw

ABSTRACT

This invention is a mechanism and design that uses headless screws that interlock with the Intramedullary Nail. Canulated outer screws engage the threads of the headless screws and further locks into the Intramedullary Nail. A sleeve on the outer end of the headless screw will aid in centering of the IM Nail. This process may be repeated contra laterally for optimal fixation and centering of the IM Nail when allowed by the anatomy. This mechanism ensures no play in the screw-nail interface which is inherent in current interlocking designs.

CROSS REFERENCE TO RELATED APPLICATIONS

Provisional Patent Application No.: 60/459,952 with a filing date ofApr. 4, 2003 (submitted by inventor of this application)

U.S. Pat. No. 6,019,761, dated Feb. 1, 2000 suggests interlocking byusing guidewire that goes in through the IM Nail holes, up or down theIM Nail and out the next hole.

U.S. Pat. No. 6,524,314, dated Feb. 25, 2003 suggests interlocking byusing 2 lag screws and a locking screw through the IM Nail.

An Intramedullary Nail (IM Nail) is inserted into the cortical bone.Standard interlocking technique is used to place each of the screws intothe nail. However, these screws are headless (versus a headed screw usedin current techniques). The screwdriver for placing the headless screwremains attached to this headless screw after insertion. A decision ismade on the length of the outer screw (the one that encapsulates theheadless screw) to be placed so that the intramedullary nail is kept ata fixed distance from the cortex of the bone.

The headless screw is then over drilled with a canulated drill. Thecanulated outer screw is then placed over the modular screwdriver andthen over the headless screw. The outer screw engages threads on thenail, locking the outer screw to the nail. The opening of the nail maybe tapered such that it allows the outer screw a perpendicular insertionto the nail. The screw may also be tapered to all interlock with the IMNail.

Additionally, a small thin sleeve may be on the outer screw that willallow for centering the headless screw in the nail opening. This willeliminate the play of the headless screw within the nail. Upon surgeon'sdiscretion, a similar outer screw can be placed from the contra lateralside where the anatomy will allow it. Having screws on opposing sides ofthe IM Nail, will help to center the nail and guarantee locking andincreases cortical purchase of the screws.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING

Not Applicable

BACKGROUND OF THE INVENTION

The current methods of fracture reduction are:

-   -   Casts/braces    -   Plates:        -   Conventional        -   Locking    -   External fixation    -   Intramedullary Nails

Intramedullary Nails have several advantages over other forms offixation:

-   -   they are less invasive than plates;    -   they have a lower infection rate;    -   nails are stronger than the plates;    -   nails have a mechanical advantage compared to plates;    -   the screws used with nails are more resistant to breakage due to        the decreased moment arm;    -   screws may be placed in different planes;    -   nails have a high rate of union;    -   nails allow for anatomic reduction;    -   cast/braces immobilize the limb and do not allow early motion;    -   external fixators have a risk of pin tract infections.

One of the current method of interlocking IM Nails is to solely usescrews, which can result in loss of reduction because of the inherentplay in screw-nail interface. A second way of interlocking IM Nails isto cap the screw at the contra lateral cortex, which increases fixationin the cortical bone; however, does not help the screw-nail interface;additionally, pressure applied by the capping on one end may cause thedistal end to move out of position. A third available way ofinterlocking IM Nails is to have the hole of the IM Nail lined withrubber to provide a more grippable material for the screws; however, theinherent play in rubber does not provide sufficient locking. The rubberline IM Nails also have the possible for foreign body reactions withflaking of the rubber.

This new design, with threaded guidewire in between the screws, locksthe screw in place to eliminate this play and result in a more stableform of fixation.

Two other patented ways of interlocking IM Nails were found, however,neither are currently marketed:

-   -   An interlocking Intramedullary Nail (U.S. Pat. No. 6,524,314,        granted Feb. 25, 2003) provides for a different mechanism, using        2 lag screws and a locking screw. This product is currently not        marketed; however, this would be a difficult mechanism because        there are only a couple of safe zones where screws can be        placed. With the addition of 2 screws placed for fixation, it        may be difficult to find safe zones. Additionally, the may cross        thread early prohibiting further insertion.    -   An interlocking Intramedullary Nail (U.S. Pat. No. 6,019,761,        granted Feb. 1, 2000) provides for interlocking by placing a        guidewire through one screw hole up to and out of the next. This        patent also relies on drilling holes versus already manufactured        holes and dropping wires through the holes and using the screws        to cause the wires to interlock to the screws. This patent has a        complete different means by which the interlocking would occur        and be enhanced.

This new mechanism, with the headless screw and outer screw, locks thescrew in place to eliminate this play and result in a more stable formof fixation. A sleeve on the outer end of the screw will aid incentering of the screw. Additionally, the option of placing an outerscrew on both sides of the IM Nail offers a possibly stronger fixationwith increased ability to center the IM Nail.

BRIEF SUMMARY OF THE INVENTION

This invention provides for a new method for locking IntramedullaryNails (IM Nails) with headless screws for performing interlocking withthe IM Nail. The headless screw is over drilled with a canulated drill.A subsequent, outer screw is placed such that it encapsulates thisheadless screw. The outer screw engages threads on the nail, locking theouter screw to the nail. This method and design eliminates play in thescrew-nail interface and result in a more stable form of fixation. Theheadless screw may also have a sleeve on the outer end which will aid incentering of the IM Nail. The outer screw may also be placed from thecontra lateral side where the anatomy will allow it.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Page 1: Diagram of Insertion of the first headless screw intoIntramedullary nail

-   -   1.Cortical bone    -   2.Intramedullary Nail    -   3.Headless screw    -   4.Modulated screwdriver

Page 2: Diagram of over drilling around the headless screw withcanulated drill.

-   -   1.Headless screw    -   2.Modulated screwdriver    -   3.Are of over drilling around headless screw    -   4.Intramedullary Nail

Page 3: Diagram of insertion and interlocking of outer screw to innerscrew and Intramedullary Nail

-   -   1.Canulated outer screw    -   2.Optional sleeve with variable length    -   3.Dotted line showing canulated outer screw to be placed over        headless screw    -   4.Engaged outer screw over headless screw    -   5.Place where outer screw interlocks with Intramedullary Nail    -   6.Intramedullary Nail    -   7.Placement of additional optional outer screw on the contra        lateral side

DETAILED DESCRIPTION OF THE INVENTION

The IM Nails and screws are manufactured with cobalt-chrome, titanium orother materials for strength and durability. The current methods do notaddress screw-nail interface locking and can cause loss in reduction. Inthis invention, the IM Nail is secured by headless screws and canulatedouter screws that cap the headless screws; this will secure andeliminate movement of the screws to the IM Nail.

The screwdriver for placing the headless screw remains attached to thisheadless screw after insertion. A decision is made on the length of theouter screw (the one that encapsulates the headless screw) to be placedso that the intramedullary nail is kept at a fixed distance from thecortex of the bone. The headless screw is then over drilled with acanulated drill. The outer screw is then placed over the modularscrewdriver and then over the headless screw. The outer screw engagesthreads on the nail, locking the outer screw to the nail. The opening ofthe nail may be tapered such that it allows the outer screw aperpendicular insertion to the nail. The screw may also be tapered suchthat it can also interlock with the IM Nail.

Additionally, a small thin sleeve may be on the outer screw that willallow for centering the headless screw in the nail opening. This willeliminate the play of the headless screw within the nail. Upon surgeon'sdiscretion, a similar outer screw can be placed from the contra lateralside where the anatomy will allow it.

Current methods of interlocking IM Nails do not eliminate the screw-nailinterface play. Therefore, current methods can result in loss ofreduction of the fracture. This method and design in locking eliminatesplay in the screw-nail interface and results in a more stable form offixation.

1. A mechanism to secure Intramedullary Nails by using headless screwsto interlock with the Intramedullary Nail with a canulated outer screwthat engages the headless screw's threads and further locks onto theIntramedullary Nail. This process may be repeated contra laterally. Thismechanism immobilizes the Intramedullary Nail to maintain fracturereduction and aids in centering of the IM Nail.